Diving Nitrox with a pony bottle - theoretical

[Graeme Fraser]

A pony (as a pure emergency air source) is almost exclusively a recreational diving tool. In the tech realm, gas planning is much more complex and you are right, a pony is insufficient for their needs.
One variation of gas planning is the rule of thirds. One third there, one third back, one third in reserve. With doubles on an isolator, if one post fails at the worst time (turn point) each of the two tanks is 2/3 full... Isolate, and you still have gas to get back. Or buddy has total catastrophic gas loss, he gets your long hose, you're "reserve" was equal to worst case return needs, so you both still have gas to get back.
This is oversimplified examples... I don't have sufficient training to go further with that.
For my non-overhead NDL diving, my 19 is actually overkill.... For tech it would be laughably insufficient.

Again, a very succinct explanation. True breathing gas redundancy should mean you, or your buddy, could lose a complete gas source but still have an alternative plan and sufficient gas to return to the surface safely whilst fulfilling your deco obligations. As your twins (doubles) tend to be your bottom gas, the ability to isolate these will satisfy this criteria, if you have factored gas lose in to your plan. Stage(s) cylinders usually contain enriched oxygen which will accelerate your decompression obligation.

 

[tursiops]

Stage(s) cylinders usually contain enriched oxygen which will accelerate your decompression obligation.

Stages extend the bottom portion of the dive, or are used as a travel gas to get to the bottom (or back up). Anything with extra O2 to accelerate deco is a deco bottle. Stages extend the dive beyond what your back (or side) gas volume is.

 

[Diver below 83]

Stages extend the bottom portion of the dive, or are used as a travel gas to get to the bottom (or back up). Anything with extra O2 to accelerate deco is a deco bottle. Stages extend the dive beyond what your back (or side) gas volume is.

thats what you’d typically see with a green(o2) regulator setup?

 

[tursiops]

thats what you’d typically see with a green(o2) regulator setup?

A green Reg/hose is most likely on a 100%O2 bottle, for deco at 20 ft and above. Other gases might be used for deco too, or instead, depending on the logistics and the dive; 50%O2 and 80%O2 are also popular. But mostly likely NOT with green regs (or hoses).

 

[Diver below 83]

A green Reg/hose is most likely on a 100%O2 bottle, for deco at 20 ft and above. Other gases might be used for deco too, or instead, depending on the logistics and the dive; 50%O2 and 80%O2 are also popular. But mostly likely NOT with green regs (or hoses).

The non green ones usually have the large stickers labeling the % of o2 in each tank correct?

 

[tursiops]

The non green ones usually have the large stickers labeling the % of o2 in each tank correct?

All the tanks should be so marked, especially the 50+% deco bottles. People have died from breathing the wrong bottle at the wrong depth.

 

[MrBigfins]

I dive a 19cf pony back mounted on every dive. I fill with air regardless of my main tank mix. My thoughts are if I find myself forced below mod on my nitrox I have a gas that's safe to breathe. I refuse to use the pony to extend dives as I have seen some do. The only exception is the last dive of a dive vacation that I flew to and from. On the last dive I will breathe pony down as I have to empty it anyways to fly. I will occasionally practice use on a normal dive and switch to it for a breath or two so that I can ensure a smooth transition if I would actually need to use it. I dive with the valve open on every dive, one less step if SHTF

 

[Graeme Fraser]

Stages extend the bottom portion of the dive, or are used as a travel gas to get to the bottom (or back up). Anything with extra O2 to accelerate deco is a deco bottle. Stages extend the dive beyond what your back (or side) gas volume is.

Strictly speaking yes. Maybe we tend to be a bit lazy over here by generally using the term stage or deco cylinder interchangeably.

 

[Diving Dubai]

Strictly speaking yes. Maybe we tend to be a bit lazy over here by generally using the term stage or deco cylinder interchangeably.

We're the same here. Anything clipped to your side is a stage or (heaven forbid) a bailout.

Pony is such a stupid term.

That cylinder clipped to me has enough gas to generally be a stage or deco or bailout depending on my needs or choices on that dive - but keep it quiet otherwise I'll be burned as a heretic

 

[tursiops]

We're the same here. Anything clipped to your side is a stage or (heaven forbid) a bailout.

Pony is such a stupid term.

That cylinder clipped to me has enough gas to generally be a stage or deco or bailout depending on my needs or choices on that dive - but keep it quiet otherwise I'll be burned as a heretic

Since we are talking definitions and semantics, a pony is not part of your gas plan....it is a bailout in case your primary gas supply is no longer available. A pony might be any size, but should be large enough to get you calmly to the surface, preferably with a safety stop. So Spare Air is not big enough, a 13 cuft is really too small, a 19 is much better, and a 30 or 40 cu ft is fine but overkill. It is not intended to be used, even if it looks like a stage and is slung like a stage, whereas a stage is part of your gas plan and is intended to be used. Call the pony a bailout if you'd like, but don't call it a stage.